Multiple-pathway optical transmitter

ABSTRACT

Optical systems comprise one or more optical pathways including lenses that are offset with respect to each other and lenses that are offset with respect to optical fibers.

BACKGROUND

1. Field of the Invention

The present invention relates generally to optical transmitters.

2. Related Art

One of the problems in fiber communications is that optical feedback,typically from the fiber to the laser, affects the laser operation andgives rise to jitter in the timing of the rising and falling edges ofthe signal. The effects of the feedback are most severe with single-modelasers, e.g. 1310 nm VCSELs or DFB lasers, but it is also significantwith multi-mode lasers, e.g. 850 nm VCSELs or Fabry-Perot (FP) lasers.Therefore, there exists a need for a way to reduce feedback forsingle-mode lasers and multi-mode lasers.

SUMMARY

According to a first broad aspect of the present invention, there isprovided a system comprising: one or more optical pathways, each opticalpathway comprising: a first lens having a first lens axis; a second lenshaving a second lens axis that is offset with respect to the first lensaxis by a lateral distance that is greater than the combinedmanufacturing tolerance of the first lens and the second lens; and anoptical fiber having a fiber axis.

According to a second broad aspect of the present invention, there isprovided a system comprising: one or more optical pathways, each opticalpathway comprising: a first lens having a first lens axis; and anoptical fiber having a fiber axis that is offset with respect to thefirst lens axis by a lateral distance that is greater than the combinedmanufacturing tolerance of the first lens and the optical fiber.

According to a third broad aspect of the present invention, there isprovided a system comprising: one or more optical pathways, each opticalpathway comprising: a first lens having a first lens axis; a second lenshaving a second lens axis that is offset by a lateral distance greaterthan 2 μm with respect to the first lens axis; and an optical fiberhaving a fiber axis.

According to a fourth broad aspect of the present invention, there isprovided a system comprising: one or more optical pathways, each opticalpathway comprising: a first lens having a first lens axis; and anoptical fiber having a fiber axis that is offset by a lateral distancegreater than 2 μm with respect to the first lens axis.

According to a fifth broad aspect of the present invention, there isprovided a system comprising: two or more optical pathways, each opticalpathway comprising: a first lens having a first lens axis; a second lenshaving a second lens axis that is offset with respect to the first lensaxis by a lateral distance that is greater than the combinedmanufacturing tolerance of the first lens and the second lens; anoptical fiber having a fiber axis; and two or more VCSELs for emittinglight through respective optical pathways of the two or more opticalpathways, wherein one or more of the VCSELs emits a lowest-order modeand one or more higher-order modes, and wherein the lowest-order modeand a higher-order mode focus at least 50 μm apart from each other.

According to a sixth broad aspect of the present invention, there isprovided a system comprising: two or more optical pathways, each opticalpathway comprising: a first lens having a first lens axis; a second lenshaving a second lens axis that is offset by a lateral distance greaterthan 2 μm with respect to the first lens axis; an optical fiber having afiber axis; and two or more VCSELs for emitting light through respectiveoptical pathways of the two or more optical pathways, wherein one ormore of the VCSELs emits a lowest-order mode and one or morehigher-order modes, and wherein the lowest-order mode and a higher-ordermode focus at least 50 μm apart from each other.

According to a seventh broad aspect of the present invention, there isprovided a system comprising: two or more optical pathways, each opticalpathway comprising: a first lens having a first lens axis; a second lenshaving a second lens axis; an optical fiber having a fiber axis that isoffset with respect to the first lens axis by a lateral distance that isgreater than the combined manufacturing tolerances of the first lens,the second lens and the optical fiber; and two or more VCSELs foremitting light through respective optical pathways of the two or moreoptical pathways, wherein one or more of the VCSELs emits a lowest-ordermode and one or more higher-order modes, and wherein the lowest-ordermode and a higher-order mode focus at least 50 μm apart from each other.

According to an eighth broad aspect of the present invention, there isprovided a system comprising: two or more optical pathways, each opticalpathway comprising: a first lens having a first lens axis; a second lenshaving a second lens axis; an optical fiber having a fiber axis that isoffset by a lateral distance greater than 2 μm with respect to the firstlens axis; and two or more VCSELs for emitting light through respectiveoptical pathways of the two or more optical pathways, wherein one ormore of the VCSELs emits a lowest-order mode and one or morehigher-order modes, and wherein the lowest-order mode and a higher-ordermode focus at least 50 μm apart from each other.

According to a ninth broad aspect of the present invention, there isprovided a system comprising: two or more optical pathways, each opticalpathway comprising: a first lens; a second lens; an optical fiber; andtwo or more VCSELs for emitting light through respective opticalpathways of the two or more optical pathways, wherein one or more of theVCSELs emits a lowest-order mode and one or more higher-order modes, andwherein the lowest-order mode and a higher-order mode focus at least 20μm apart from each other.

According to a tenth broad aspect of the present invention, there isprovided a system comprising: two or more optical pathways, each opticalpathway comprising: a first lens; a second lens; an optical fiber; andtwo or more VCSELs for emitting light through respective opticalpathways of the two or more optical pathways, wherein one or more of theVCSELs emits a lowest-order mode and one or more higher-order modes, andwherein the lowest-order mode and a higher-order mode focus at least 50μm apart from each other.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a schematic view of an offset launch of light into amulti-mode fiber looking down the fiber core;

FIG. 2 is a schematic side view of the offset launch of FIG. 1 taken inthe direction of arrow 2 of FIG. 1;

FIG. 3 is a schematic side view of the offset launch of FIG. 1 taken inthe direction of arrow 3 of FIG. 1;

FIG. 4 is a schematic view of an offset launch of light into amulti-mode fiber looking down the fiber core;

FIG. 5 is a schematic side view of the offset launch of FIG. 1 taken inthe direction of arrow 5 of FIG. 4;

FIG. 6 is a schematic side view of the offset launch of FIG. 1 taken inthe direction of arrow 6 of FIG. 4;

FIG. 7 is a schematic cross-sectional view of an optical systemincluding an aligned OSA;

FIG. 8A is a schematic cross-sectional view of the optical system with aVCSEL tilted to form an angled emitted light beam and angled reflectedlight beam;

FIG. 8B shows the path of the emitted light beam and reflected lightbeam of the optical system of FIG. 8A, with proportions of the featuresof the system altered to better show the angular paths of the emittedand reflected light beams;

FIG. 9A is a schematic cross-sectional view of an optical system with aVCSEL and an OSA focusing two different modes at different locationsaccording to one embodiment of the present invention;

FIG. 9B shows the path of the emitted light beam and reflected lightbeam for the lowest order mode of the optical system of FIG. 9A, and theemitted light beam from a higher order mode, with proportions of thefeatures of the system altered to better show the angular paths of theemitted and reflected light beams.

FIG. 10 is a schematic illustration of an optical system according toone embodiment of the present invention;

FIG. 11A is a schematic illustration of an optical system according toone embodiment of the present invention;

FIG. 11B is a close-up illustration of a portion of the optical systemof FIG. 11A to better show the angle of incidence of the reflected beamon the VCSEL of the optical system; and

FIG. 12 is schematic illustration of a lens array of the presentinvention;

DETAILED DESCRIPTION

It is advantageous to define several terms before describing theinvention. It should be appreciated that the following definitions areused throughout this application.

DEFINITIONS

Where the definition of terms departs from the commonly used meaning ofthe term, applicant intends to utilize the definitions provided below,unless specifically indicated.

For the purposes of the present invention, the term “unibody” refers toa device that is constructed of one primary element, as opposed to twoor more elements assembled, or removably connected.

For the purposes of the present invention, the term “constructedintegrally” refers to a device that has been constructed to includemultiple parts having various functions, where the multiple pieces maynot be separated from the remainder of the device without damaging thedevice.

For the purposes of the present invention, the term “diffractiveelement” refers to an element that decomposes a light beam intosub-beams to redirect the light into directions corresponding toconstructive interference between the sub-beams, wherein each of thesub-beams has a phase difference of an integral number of wavelengthsnot equal to zero. A diffractive element typically comprises a largenumber of sub-elements that each has a width on the order of an opticalwavelength of the light diffracted by the element. A diffractive elementmay be composed of multiple diffractive elements. Examples ofdiffractive elements are described in U.S. Pat. Nos. 6,530,697;6,496,621; and 6,600,845, the entire contents and disclosures of whichare hereby incorporated by reference.

For the purposes of the present invention, the term “refractive element”refers to an element that does not decompose a light beam, but after thelight beam passes through the refractive element all of the portions thelight beam have substantially zero phase difference. An element may actas a refractive element due to: the shape of the refractive element, theangle at which a light strikes the refractive element, variation in therefractive index of the refractive element, etc. A refractive elementmay be composed of multiple refractive elements.

For the purposes of the present invention, the term “axial alignment”refers to two or more items that all lie along the axis of at least oneof the items to permit light to pass through each of the items. Forexample, FIG. 7 illustrates an example of a TOSA in which the VCSEL,lens, barrel receptacle and optical fiber are in axial alignment alongthe long axis of the barrel receptacle. Two items that are in axialalignment are “coaxial.”

For the purposes of the present invention, the term “laser end” or“proximal end” refers to end of an optical subassembly where a laser islocated.

For the purposes of the present invention, the term “fiber end” or“distal end” refers to the end of an optical subassembly where a fiberis inserted into the sub-assembly or where a fiber may be inserted intothe sub-assembly.

For the purposes of the present invention, the term “lowest-ordertransverse mode” refers to the beam emitting from the central portion ofthe VCSEL aperture, usually originating from a single region in theaperture and usually having a relatively small divergence angle.

For the purposes of the present invention, the term “higher-ordertransverse mode” refers to any beam emitting from a non-central portionof the VCSEL aperture, usually originating from multiple regions in theaperture and usually having a divergence angle larger than that of thelowest-order transverse mode.

For the purposes of the present invention, the term “radial” refers to adirection either toward or away from the center an optical aperture.

For the purposes of the present invention, the term “azimuthal” refersto a direction oriented at a right angle to a radius from the center ofan optical aperture.

For the purpose of the present invention, the term “chordial” refers toa direction along any chord of an optical aperture i.e. a direction thatis non-radial. A purely azimuthal direction is a chordial direction thathas no radial component.

For the purposes of the present invention, the term “optical scattering”refers to the deflection of light from the path it would follow if therefractive index were uniform or gradually graded. Scattering is causedprimarily by microscopic or submicroscopic fluctuations in therefractive index or surface.

DESCRIPTION

It has been found experimentally, with parallel optical modules, thatmisalignment can reduce the effects of feedback with multi-mode 850 nmVCSEL arrays. The effect of misalignment is that the misaligned beam isincident on the fiber at an angle. In fact, intentionally tilting theVCSEL array produces a similar reduction of feedback effects. For anidealized optical system, the reflected light beam should propagatedirectly back to the VCSEL aperture. Non-ideal systems, e.g. those usinga ball lens or other non-ideal lens, may have the beam distorted on thereturn, which may reduce feedback effects, but only slightly. For amulti-mode VCSEL in a misaligned system or one with the tilted VCSEL,the effects of feedback may be reduced since the reflected light beamincident on the VCSEL will be at a different angle from the emittedlight beam.

An objective of the present invention is to produce an opticalsub-assembly (OSA) in which the effects of optical feedback are reduced.In a manufacturing environment, it is undesirable to have misalignmentor tilting of the laser source. It is therefore a further objective ofpresent invention to provide an optical sub-assembly in which the laser,e.g. VCSEL, does not need to be tilted, and in which misalignment isminimized. It is yet another objective of the present invention toproduce and OSA in which the effective modal bandwidth of a multi-modefiber is improved.

Feedback effects may be decreased and the effective modal bandwidth(MBW) may be increased by an optimized launch condition. In GigabitEthernet, even the 500 MHz-km MBW is achieved by an “offset launch” inwhich light from a single-mode fiber is coupled into a 62.5 μm diameterMMF fiber offset by ˜23 μm from the center. Such an offset launch 102 isshown in FIGS. 1, 2, and 3 showing a fiber core 112 into which islaunched a light beam 114 that is offset from optical axis 118 of fibercore 112. FIGS. 1, 2 and 3 show three views of launch 102: looking downfiber core 102 (FIG. 1), looking at the side of fiber core 112 (FIG. 2,the direction of arrow 2 of FIG. 1), and looking at the side of fibercore 112 from an angle 90° rotated from the view of FIG. 2 (FIG. 3, thedirection of arrow 3 of FIG. 1). This launches the light away from theinnermost and outermost modes, but after propagating some distance inthe fiber, the light may redistribute and couple into some of theundesired modes, particularly the innermost modes.

The effective MBW may be further improved by introducing an azimuthalangle to the launch into the fiber, for example an angle between 1 and10 degrees. Such an angled offset launch 402 is shown in FIGS. 4, 5, and6 showing a fiber core 412 into which is launched a light beam 414 thatenters fiber core 412 at a point 416 offset from optical axis 418 offiber core 412. As shown in FIG. 6, light beam 414 is launched intofiber core 412 at an angle 602 to a vertical line 604 extending fromoptical axis 418. Together FIGS. 4, 5 and 6 show three views of launch402: looking down fiber core 412 (FIG. 4), looking at the side of fibercore 412 (FIG. 5, the direction of arrow 5 of FIG. 1), and looking atthe side of fiber core 414 from an angle 90° rotated from the view ofFIG. 5 (FIG. 6, the direction of arrow 6 of FIG. 1).

The azimuthal angular component to the launch shown in FIGS. 4, 5 and 6minimizes the coupling into the innermost modes, since the light tendsto propagate in a spiral pattern down the fiber. The “offset azimuthallaunch” may be accomplished by 1) introducing the azimuthal angle intothe optical subassembly; 2) aligning to a single-mode fiber; 3)laterally translating the laser by a distance which produces the desiredlateral offset; and 4) setting the components in place. The angularincidence of the beam onto the fiber will reduce the effects of thereflected light beam on the VCSEL, especially if it is a multi-modeVCSEL. Tilting the VCSEL will cause the beam incident on the fiber to beat an angle. If the displacement is in a direction orthogonal to theplane defined by the beam and the optical axis of the fiber, then theangle will be in an azimuthal orientation.

FIG. 7 shows an example of an optical system 700 including an alignedOSA 702 including a lens 712 and a fiber receptacle 714 for receiving anoptical fiber 716 having a fiber core 718, a fiber axis 720, and a flatfiber distal end 722. Fiber receptacle 714 has a cylindrical interiorsurface 728 having an interior surface distal end 730 that includes acylindrical recess 732 having a straight lens rear surface 734, whichmay be optically flat, concave, convex, faceted, or any other shape. Anemitted light beam, indicated by right-pointing arrowhead 742, isemitted from an aperture 744 of a flat mounted VCSEL 746, travelsthrough lens 712 and becomes incident on fiber distal end 722 at fiberaxis 720. A portion of the emitted light beam is reflected by fiberdistal end 722 as a reflected light beam, indicated by left-pointingarrowhead 756, and is returned straight back, along optical axis 758,into an aperture 744 of VCSEL 746. Optical fiber 714 includes a flatdistal end 722 that reflects the emitted light beam. Lens rear surface734 is considered “straight” because lens rear surface 734 isperpendicular to fiber axis 720 and optical axis 758 that extends alongfiber axis 720.

In FIG. 7, the reflected light beam may enter the VCSEL aperture andinterfere with the light being generated by the VCSEL, with constructiveand destructive interference varying rapidly, thereby causing intensityfluctuations in the emitted light beam, which gives rise to noise andjitter in the signal.

FIGS. 8A and 8B show the effect of tilting the VCSEL 746 of FIG. 7. Inoptical system 800, an emitted light beam 842 propagates at an angle 844with respect to optical axis 758. Emitted light beam 842 is refracted bylens 712 to make an angle 846 with optical axis 758 and becomes incidenton fiber distal end 722 at fiber axis 720. A portion of emitted lightbeam 842 is reflected by fiber distal end 722 to form reflected lightbeam 856. Reflected light beam 856 is reflected at an angle 860 withrespect to optical axis 758. Reflected light beam 856 is refracted bylens 712 so that reflected light beam 856 enters the aperture (notshown) of VCSEL 746 at an angle 862 with respect to optical axis 758.Reflected light beam 856 is incident on VCSEL aperture 744 at a relativeangle 866 (the sum of angles 844 and 862) that is two times angle 844,the tilt angle of VCSEL 746.

In a system such as shown in FIGS. 8A and 8B, the reflected light beammay be degraded relative to the emitted light beam due to the doublepass through the lens system. The angle between the emitted andreflected beams produces variation in the constructive and destructiveinterferences, thereby decreasing the overall intensity fluctuations. Alens system having some aberrations is also likely to result in lessfeedback than a perfect lens. Also, as mentioned earlier, tilting ofcomponents is undesirable in a manufacturing environment. Ways ofproducing a variety of improved optical systems will now described.

FIGS. 9A and 9B show an optical system 900 including an OSA barrel 902including a lens 912 and a fiber receptacle 914 for receiving an opticalfiber 916 having a fiber core 918, a fiber axis 920, and a flat fiberdistal end 922. Fiber receptacle 914 has a cylindrical interior surface928 having an interior surface distal end 930 that includes acylindrical recess 932 having a lens rear surface 934. VCSEL 938 ismounted flat and has an aperture 940 that is approximately centered withrespect to fiber axis 920 and optical axis 946. An emitted light beam950 from a fundamental or lowest-order mode is represented by rays 952and 954 from aperture 940 of VCSEL 938 which diverge until emitted lightbeam 950 is refracted by lens 912 to converge as represented by rays 956and 958. Then, emitted light beam 950 is refracted by lens rear surface934 along a slightly more convergent path until emitted light beam 950is incident on flat fiber distal end 922. As shown, emitted light beamis not focused on flat fiber distal end 922, but is focused inside fibercore 918 at plane 966 at focus position 968. A portion of emitted lightbeam 952 is then reflected from fiber distal end 922 as reflected lightbeam 960, represented by light rays 962 and 964. Reflected light beam960 is refracted by lens rear surface 934 and by lens front surface 912.Reflected light beam 960 is then incident on the aperture 940 of VCSEL938. Due to the defocusing of emitted light beam 950 on flat fiberdistal end 922, reflected light beam 960 is even more defocused onaperture 940 and is shown in FIG. 9B to have a diameter D which is muchlarger than the diameter of aperture 940. Thus, most of reflected lightbeam 960 does not enter aperture 940, and the effects of opticalfeedback are reduced.

An emitted light beam 980 from a higher-order mode is represented byrays 982 and 984 from aperture 940 of VCSEL 938 which diverge untilemitted light beam 980 is refracted by lens 912 to converge asrepresented by rays 986 and 988. Then, emitted light beam 980 isrefracted by lens rear surface 934 along a slightly more convergent pathuntil emitted light beam 980 is incident on flat fiber distal end 922 atfiber axis 920. As shown, the emitted light beam from the higher-ordermode is approximately focused on flat fiber distal end 922. A portion ofemitted light beam 980 is then reflected from fiber distal end 922.Although not shown, the reflection of emitted light beam 980 of ahigher-order mode is refracted by lens rear surface 934 and by lensfront surface 912. Reflected light from emitted light beam 980 is thenincident on the aperture 940 of VCSEL 938. VCSEL 938 is not as sensitiveto reflections from a higher-order mode as it is from the lowest-ordermode. The distance X, shown in FIG. 9B is defined as the distancebetween the focus position 968 of the lowest-order transverse mode and afocus position 992 of a higher-order transverse mode.

In the optical system shown in FIGS. 9A and 9B, aberrations from thelight beam pathways shown may be due to aberrations in the lens designand/or alignment between the components of the system. A sphericallyshaped lens 912 qualitatively produces the focusing characteristicsshown in FIGS. 9A and 9B, which may reduce the feedback effects thoughperhaps not optimally. While spherically-shaped ball lenses were used inthe past for VCSEL OSAs and are often used for single-mode OSAs,molded-plastic TOSAs such as the OSA shown in FIG. 9A employ asphericalsurfaces which focus all rays from the emitted beam in approximately thesame plane. Without the present inventive concept, it would becounter-intuitive for one skilled in the art to design an OSAdeliberately with aberrations or even a spherical surface when it isstraightforward to manufacture an “improved” aspherical surface. In U.S.Pat. No. 5,319,496, Jewell et al., the entire contents and disclosure ofwhich is hereby incorporated by reference, describes the use ofaberrations to focus multiple VCSEL modes onto a smaller spot area. Thepresent invention is opposite in nature in that the multiple modes aredeliberately focused at different locations. The application andcharacteristics of the present invention differ greatly from that ofU.S. Pat. No. 5,319,496. Some advantageous characteristics of an OSA ofthe present invention, such as the OSA of FIG. 9A, to be advantageousare: 1) the coupling efficiency into the fiber of the lowest-order modeis most tolerant to misalignment, e.g. defocus or displacement; 2) theVCSEL is most sensitive to feedback from the lowest-order mode. An OSAof the present invention may reduce the effects of feedback withoutsacrificing coupling efficiency.

Although in the embodiment shown in FIGS. 9A and 9B in which the focusposition of the lowest-order transverse mode is inside the fiber, inanother embodiment the focus position of the lowest-order transversemode may be outside the fiber and/or the focus position of ahigher-order transverse mode may be inside or outside the fiber.

In one embodiment, the present invention provides an OSA in which thedistance between the focus point for the lowest-order transverse modeand for a higher-order transverse mode is 20 μm or more. In anotherembodiment, the present invention provides an OSA in which the distancebetween the focus point for the lowest-order transverse mode and for ahigher-order transverse mode is 50 μm, or more. One property of a lensthat may cause the distance between the lowest-order transverse modefocus point and a higher-order transverse mode focus point to besignificant is spherical aberration. Normally lenses are designed tohave minimal spherical aberration, for example less than one quarterwave. In one embodiment the present invention employs an OSA with a lenshaving more than one half wave of spherical aberration.

Although the lens rear surface in the embodiment of the presentinvention shown in FIGS. 9A and 9B is optically flat, the lens rearsurface may be concave, convex, faceted, or any other shape, such as thelens rear surface shapes described and shown in U.S. patent applicationSer. No. 12/042,062 to Jewell et al. entitled “Low-Noise OpticalTransmitter,” filed Mar. 4, 2008, the entire contents and disclosure ofwhich is hereby incorporated by reference.

FIG. 10 illustrates a multi-channel optical system 1002 according to oneembodiment of the present invention in which an emitted light beam 1004from a VCSEL 1012 travels through proximal lens surface 1016 and adistal lens surface 1018 that focus emitted light beam 1004 on fiber1020. A portion of the light of emitted light beam 1004 is reflectedback as reflected light beam 1022 that travels through distal lenssurface 1018 and proximal lens surface 1016 to become incident on VCSEL1012. Fiber 1020 has a fiber axis 1024, proximal lens surface 1016 has alens axis 1026, and distal lens surface 1018 has lens axis 1028. As canbe seen in FIG. 10, lens axis 1026 is displaced from lens axis 1028 by adisplacement 1030. In the example of FIG. 10, lens axis 1028 isapproximately coincident with fiber axis 1024.

The proximal lens surface and distal lens surface of FIG. 10 may be aunibody device, or be constructed integrally, or be completely separate.

FIG. 10 shows how a displacement between the lens axes of a 2-lenssurface optical system may be used to produce an angle of incidence ofthe reflected light beam onto the VCSEL. The effect is similar totilting the VCSEL, but may be simpler to implement in manufacturing. InFIG. 10, only one channel of optical system 1002 is shown, with onlyportions of the lenses shown. To minimize aberrations for the beamincident on the fiber, the VCSEL and emitted light beam is aligned withthe axis of the proximal lens surface, and the axis of the distal lenssurface is aligned with the fiber axis. Optical system 1002 mayalternatively or additionally have aberrations to focus a light beamsimilarly to the optical system shown in FIGS. 9A and 9B.

In one embodiment of the present invention, the intentional misalignmentof the proximal and distal lens surfaces axes relative to each otherprovides a displacement or offset greater than the combinedmanufacturing tolerances of the proximal and distal lenses. Factors thataffect manufacturing tolerances of the lenses include: expansion and/orcontraction of the lenses or the various parts of the optical system,imperfections in the manufacturing of the lenses or other parts of theoptical system, etc. In one embodiment the combined manufacturingtolerance for the lenses is 2 μm.

FIGS. 11A and 11B illustrate a multi-channel optical system 1102according to one embodiment of the present invention in which an emittedlight beam 1104 from a VCSEL 1112 travels through proximal lens surface1116 and a distal lens surface 1118 that focus emitted light beam 1104on fiber 1120. A portion of the light of emitted light beam 1104 isreflected back as reflected light beam 1122 that travels through distallens surface 1118 and proximal lens surface 1116 to become incident onVCSEL 1112. Fiber 1120 has a fiber axis 1124, proximal lens surface 1116and distal lens surface 1118 have a common lens axis 1126, and VCSEL1112 has a VCSEL axis 1128. As can be seen in FIG. 11A, lens axis 1126is displaced from fiber axis 1122 by a displacement 1130. Displacement1130, combined with the displacement of VCSEL axis 1128 from lens axis1126, produces an angle of incidence 1142 of reflected light beam 1122on VCSEL 1112.

In FIG. 11A, only one channel of optical system 1102 is shown, with onlyportions of the lenses shown. The proximal lens surface and distal lenssurface of FIG. 11 may be a unibody device, or be constructedintegrally, or be completely separate. Optical system 1102 mayalternatively or additionally have aberrations to focus a light beamsimilarly to the optical system shown in FIGS. 9A and 9B.

Not shown in FIGS. 11A and 11B are alignment pins monolithicallyintegrated with the lenses themselves or integrated within a lens arrayassembly for positioning a fiber array. Such alignment pins are used inthe “MT ferrule,” or similar connectors. Such alignment pins are usuallywell aligned with the lens arrays, and perfect alignment is sought.

FIGS. 11A and 11B show that it is possible to produce an angle ofincidence for the reflected light beam onto the VCSEL by laterallydisplacing the pins from the lens array, even if opposing lens surfaceaxes are perfectly aligned. FIG. 12 shows a lens array 1202 including anarray 1212 of lenses 1214. Pin centers 1222 and 1224 of respectivealignment pins 1226 and 1228 are displaced vertically from lens arrayaxis 1232 by a displacement 1234.

In one embodiment of the present invention, the intentional misalignmentof the lens axis of the lens surfaces relative to the fiber axisprovides a displacement or offset greater than the combinedmanufacturing tolerances of the lenses and the optical fiber. Factorsthat affect manufacturing tolerances of the lenses and optical fiberinclude: expansion and/or contraction of the lenses and/or optical fiberor the various parts of the optical system, imperfections inmanufacturing of the lenses and/or optical fiber or other parts of theoptical system, etc. In one embodiment the combined manufacturingtolerance for the lenses and the optical fiber is 2 μm.

EXAMPLE Example

An optical system is made as shown in FIGS. 1A and 11B. An opticalplastic material, tradenamed Ultem, is molded with the lens surfaces oneither side. The thickness of the Ultem between the lens surfaces is1.125 mm. For this system, a displacement of 13 μm between the surfacesproduces a ˜6° angle of incidence of the reflected light beam onto theVCSEL. A similar system may also be produced in glass or other opticalmaterial, for example by a wafer processing technique. Many alignmentconfigurations are possible. For any lens fabrication technology,perfect alignment of the lens axes is usually sought, and accuracies ofabout 2 μm are often achieved. Therefore, an intentional misalignment ofthe lens surface axes that is greater than the manufacturing toleranceis typically greater than 2 μm.

All documents, patents, journal articles and other materials cited inthe present application are hereby incorporated by reference.

Although the present invention has been fully described in conjunctionwith several embodiments thereof with reference to the accompanyingdrawings, it is to be understood that various changes and modificationsmay be apparent to those skilled in the art. Such changes andmodifications are to be understood as included within the scope of thepresent invention as defined by the appended claims, unless they departtherefrom.

1. A system comprising: one or more optical pathways, each opticalpathway comprising: one or more laser sources for generating light; aninput port for inputting the light; an integrally constructed lenshaving a proximal lens surface having a proximal axis, and a distal lenssurface having a distal axis that is offset with respect to the proximalaxis by a lateral distance; and an optical fiber having a fiber axis;wherein the lateral distance is such that coupling of light inputtedinto the input port and reflected from the optical fiber back into theinput port is lessened compared with coupling of light back into theinput port at a zero lateral distance between the proximal and thedistal axes of the integrally constructed lens: and wherein inoperation, the one or more of the laser sources emits a lowest-ordermode and one or more higher-order modes, wherein the lowest-order modeand a higher-order mode are focused by the corresponding integrallyconstructed lens at least 50 μm apart from each other.
 2. The system ofclaim 1, wherein the system comprises two or more optical pathways. 3.The system of claim 2, wherein the one or more laser sources comprisestwo or more VCSELs for emitting light through respective opticalpathways of the two or more optical pathways.
 4. The system of claim 1,further comprising a VCSEL having an optical axis, for emitting lightthrough one of the optical pathways, wherein the VCSEL is coaxial withthe corresponding proximal lens surface, and wherein the optical fiberis coaxial with the corresponding distal lens surface.
 5. The system ofclaim 4, wherein the system comprises two or more optical pathways. 6.The system of claim 5, wherein in operation, the VCSEL emits alowest-order mode and one or more higher-order modes, wherein thelowest-order mode and a higher-order mode are focused by thecorresponding integrally constructed lens at least 20 μm apart from eachother.
 7. The system of claim 5, wherein in operation, the VCSEL emits alowest-order mode and one or more higher-order modes, wherein thelowest-order mode and a higher-order mode are focused by thecorresponding integrally constructed lens at least 50 μm apart from eachother.
 8. The system of claim 1, wherein the integrally constructed lensis a unibody lens.
 9. A system comprising: two or more optical pathways,each optical pathway comprising: an integrally constructed lens having aproximal lens surface having a proximal axis, and a distal lens surfacehaving a distal axis that is offset with respect to the proximal axis bya lateral distance; and an optical fiber having a fiber axis; and aVCSEL for emitting light through the corresponding optical pathwaywherein in operation, the VCSEL emits a lowest-order mode and one ormore higher-order modes, wherein the lowest-order mode and ahigher-order mode focus at least 50 μm apart from each other; andwherein the lateral distance is such that light reflection from theoptical fiber into the VCSEL is lessened compared with light reflectionfrom the optical fiber into the VCSEL at a zero lateral distance betweenthe proximal and the distal axes of the integrally constructed lens. 10.The system of claim 9, wherein the integrally constructed lens is aunibody lens.
 11. A system comprising: two or more optical pathways,each optical pathway comprising: an integrally constructed lens having aproximal lens surface having a proximal axis, a distal lens surfacehaving a distal axis that is offset by a lateral distance greater than 2μm with respect to the proximal axis, and an optical fiber receptaclehaving a fiber axis; and a VCSEL for emitting light through thecorresponding optical pathway, wherein in operation, the VCSEL emits alowest-order mode and one or more higher-order modes, wherein thelowest-order mode and a higher-order mode are focused by the integrallyconstructed lens at least 50 μm apart from each other.
 12. The system ofclaim 11, wherein the integrally constructed lens is a unibody lens. 13.A system comprising: two or more optical pathways, each optical pathwaycomprising: an integrally constructed lens having a proximal lenssurface having a proximal axis, and a distal lens surface having adistal axis; an optical fiber having a fiber axis that is offset withrespect to the proximal axis by a lateral distance of at least 2 μm; anda VCSEL for emitting light through the corresponding optical pathway,wherein in operation, the VCSEL emits a lowest-order mode and one ormore higher-order modes, wherein the lowest-order mode and ahigher-order mode are focused by the integrally constructed lens atleast 50 μm apart from each other.
 14. The system of claim 13, whereinthe integrally constructed lens is a unibody lens.
 15. A systemcomprising: two or more optical pathways, each optical pathwaycomprising: an integrally constructed lens having a proximal lenssurface having a proximal axis, a distal lens surface having a distalaxis, and an optical fiber receptacle having a fiber axis that is offsetby a lateral distance greater than 2 μm with respect to the proximalaxis; and a VCSEL for emitting light through the corresponding opticalpathway, wherein in operation, the VCSEL emits a lowest-order mode andone or more higher-order modes, wherein the lowest-order mode and ahigher-order mode are focused by the integrally constructed lens atleast 50 μm apart from each other.
 16. The system of claim 15, whereinthe integrally constructed lens is a unibody lens.